This invention relates to easy opening containers or cans which may be opened by hand without benefit of an opening tool.
The most commercially successful easy opening cans utilize a tab which is formed by scoring a can end panel and removed by grasping a ring attached thereto and ripping of the tab from the end panel along the score lines. Aluminum is usually utilized for ring-tab ends of this type because of its soft and malleable qualities which allow the use of substantial residual scoring depths while still permitting removal of the tabs by hand.
However, aluminum can ends are objectionable from a number of standpoints. Aluminum is expensive and of relatively low strength as compared with a metal such as steel so that large quantities of aluminum must be utilized to provide can ends of sufficient gauge to withstand internal pressures generated within the cans. In addition, aluminum is expensive relative to steel, and aluminum can ends are also undesirable as compared with steel from an ecological standpoint since aluminum is not readily degradable. Furthermore, aluminum can ends are often utilized with steel can bodies and this combination is undesirable since an electrochemical reaction may be set up within the can due to its dual metallic nature, thereby creating the risk that the contents within the container may become contaminated.
In view of the foregoing difficulties with the easy opening can ends made from aluminum, rather substantial efforts have been made to develop an easy opening can end design which would be suitable for use with other metal ends such as steel ends. A number of proposed prior art designs have involved the use of metal or plastic plugs which are inserted into dispensing openings and vent holes of can ends which may comprise a metal other than aluminum such as steel.
U.S. Pat. No. 3,800,971 - LaVista discloses an easy opening can end having a push-in plug closing a dispensing opening. The edges of the metal push-in plug as well as the edges of the can end surrounding the dispensing opening are exposed to the contents of the container and there is no vent hole or plug for closing the vent hole. U.S. Pat. No. 3,662,914 - Slade discloses an easy opening can end with a unitary pull-out plug for the dispensing opening as well as the vent hole where the edge of the can end at the dispensing opening and the vent hole are covered by the dispensing opening and the vent hole plug portions. U.S. Pat. No. 1,190,043 - Thompson et al discloses a push-in plug which contacts the edge of an end panel surrounding the opening. However, there is no sealing engagement between the end panel and plug which would isolate the edge surrounding the opening so as to avoid exposing the contents of the container to this edge.
U.S. Pat. No. 3,756,448 - Moller et al discloses a plastic unitary pull-out plug member similar to that disclosed in the Slade patent. The edges of the opening in the Moller et al can end are covered by a rim comprising a plastic material. A similar plastic unitary plug for closing a dispensing opening spaced from a vent hole opening is disclosed in U.S. Pat. No. 3,744,662 - Zundel.
U.S. Pat. No. 3,759,206 - Dalli et al discloses can ends having integrally connected, push-in tab members. The interior of the end at the edge of the opening is covered with a sealing material to isolate the edge of the opening as well as the edge of the tabs and the contents within the can. U.S. Pat. No. 2,842,295 - Bajada discloses push-in plugs which are press fitted into openings which snugly and sealingly engage a vertically extending flange leading to the edge of the opening.